JPH03274523A - Color separation prism - Google Patents

Abstract

PURPOSE:To obtain a solid-state image pickup device which does not cause a color shading without lowering a sensitivity by arranging an interference film having the same spectral characteristics as a color separating film between the color separating film and a solid-state image pickup element in such a way that the interference film is inclined opposite to the color separating film with respect to an optical axis. CONSTITUTION:When the interference film 34 is more closely arranged on the side where magenta component light is projected than the color separating film 32, the interference film 34 having the same spectral characteristics as the color separating film 32 is used, and the color separating film 32 and the interference film 34 are arranged in such the way that they are inclined in the opposite direction with respect to the optical axis. Consequently, the spectral transmissivity of the color separating film 32 for light beams 3a-3c made incident on the color separating prism 30 respectively corresponds to transmissivity curves 4a-4c, and the spectral transmissivity of the interference film 34 respectively corresponds to 4a and 4b. Thus, the color balance of an edge on a defocusing part on a screen and the color balance in the periphery of the screen are improved by using the color separating prism to which the interference film having the same spectral characteristics as the color separating film in such a way that the interference film is inclined in the opposite direction of color separating film with respect to the optical axis is arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color separation prism used in a multi-plate imaging device. More specifically, the present invention relates to a color separation prism that eliminates the dependence of light on incident angle.

2. Description of the Related Art Generally, in a multi-plate imaging device, a color separation prism separates an incident light beam from a subject into a plurality of light beams according to the wavelength, and each of the divided light beams is received by a plurality of solid-state image sensors. There is.

For example, an example of the configuration of an optical system of a two-plate image pickup device is shown in FIG. 1, and the function of a color separation prism in a conventional multi-plate image pickup device will be explained.

In the figure, (11) is a lens, (12) is an infrared cut filter, (13) is a color separation prism, and (14) and (15) are solid-state image sensors. (13b) is a color separation film that has the property of reflecting green light and transmitting magenta light (red light, blue light). The incident light flux from the subject is transmitted through the lens (1
1) The green component of the incident light passes through the infrared cut filter (12) and enters the surface (13a) of the color separation prism (13), and is reflected by the color separation film (13b). Further, it is totally reflected by the surface (13a), reaches the solid-state image sensor (14), and generates a green signal G. Of the light incident on the color separation prism, the magenta component (red component and blue component) is
Through the color separation film (13b), the solid-state image sensor (15)
reach. Filters that transmit only red light and filters that transmit only blue light are arranged alternately in a strip shape (not shown) on the entire surface of the pixel of the solid-state image sensor (X5). The light reaching 15) is thereby decomposed into a red component and a blue component, generating a red signal (R) and a blue signal (B).

However, when capturing an image of a subject using the optical system described above,
There is a problem in that even if color balance is achieved in a certain state, the color balance is disrupted in a different state. For example, when the color balance is adjusted to the center of the screen in a focused state, the achromatic subject becomes colored in the following cases.
``color shooting'') may occur.

■ Regardless of the position within the screen, the edges of achromatic objects appear colored in areas that are out of focus (hereinafter referred to as ``defocus areas'').

■ Even if the [Bin] is correct, achromatic objects appear colored around the screen.

A technique that tries to solve the problem by correcting color shading using a circuit is disclosed in Japanese Patent Application Laid-Open No. 63-276992, but it is not effective for coloring the edges of an achromatic object in the defocused area. do not have.

Problems to be Solved by the Invention The present invention has been made in view of the above circumstances.
An object of the present invention is to provide a solid-state imaging device that does not cause color shading.

A further object of the present invention is to provide a solid-state imaging device that can achieve the above object without reducing sensitivity.

Means for Solving the Problem The above purpose is to provide an interference film having the same spectral characteristics as the color separation film between the color separation film and the solid-state image sensor in the color separation prism used in the conventional solid-state imaging device. 1. With respect to the optical axis,
This is achieved by arranging the color separation film at an angle opposite to that of the color separation film.

That is, the present invention provides a color separation prism that is used in a multi-plate imaging device and separates an incident light beam into a plurality of light beams according to wavelength, wherein the color separation prism at least separates the incident light into a green component and a magenta component. It consists of a color separation film and an interference film placed on the magenta component light output side of the color separation film, the interference film has the same spectral characteristics as the color separation film, and the color separation film and the interference film are arranged with respect to the optical axis. This is achieved by color separation prisms characterized in that they are arranged and configured to be tilted in opposite directions.

Aihocho FIG. 2 shows an example of the configuration of the color separation prism of the present invention. In the figure, (30) is a color separation prism, (31) is a light incidence surface, (
32) is a color separation film, (33) is a light exit surface, and (34) is an interference film. The interference film (34) is made of the same material as the color separation film (32). The constituent members of the color separation prism (30) are not particularly limited as long as they can achieve the effects described below, and any known components can be used.The color separation film (32) C' is the angle that C' makes with the plane perpendicular to the optical axis, and C' is the angle that the interference film (34) makes with the plane perpendicular to the optical axis. The color separation II (32) interference films (34) are tilted in opposite directions with respect to the optical axis. − and ζ′ are the same angle.

The color separation prism of the present invention can be used in place of the conventional color separation prism (13) shown in FIG.

The color separation film (32) separates the incident light from the subject that has passed through the lens (l l) 8 and the infrared cut filter (12) into a green component (hereinafter referred to as "G component J") and a magenta component (hereinafter referred to as "G component J"). It functions to decompose into RB components (as mentioned above).

In this specification, RB toward the solid-state image sensor (15)
It is explained that the G component can be completely decomposed into the acid component and the solid-state image sensor (14).

FIG. 3 shows a color separation prism having the same configuration as the color separation prism shown in FIG. 2 except that the interference film (34) is not provided, and the characteristics of the color separation film will be further explained.

The spectral transmittance of a light beam passing through a color separation film is dependent on the angle of incidence. Incident light rays with different angles of incidence on the color separation film (2a)
The spectral transmittance of the color separation film (32) for , (2b) and (2C) is shown in the curves (4a) and (4) shown in FIG. 4, respectively.
b), (4C).

In the solid-state image sensor (15), the part where the red filter is arranged is called the R channel, and the part where the blue filter is arranged is called the B channel. The spectral sensitivities of the R channel and B channel when directly irradiated are shown by curves 5R and 5B in FIG. 5, respectively. An interference film (34
) The spectral sensitivities of the R channel and B channel of the light that has passed through the color separation prism (30) shown in FIG. The symbol in FIG. 6, for example 5Ra, indicates the light ray (2a) (
The spectral sensitivity curve of the R channel corresponding to FIG. 3) is shown. In other words, the incident ray (the third
) and the spectral curves in FIG. 6 correspond to lowercase letters a, b, and c.

As can be seen from this figure, when the angle of incidence on the color separation film (32) differs, the spectral sensitivity also differs. This is because, as described above, the spectral transmittance of the color separation film is dependent on the angle of incidence. In FIG. 6, the area of the region between the curve and the horizontal axis represents the sensitivity to equal-energy white light, and the sensitivity of the solid-state imaging device corresponding to the light ray 2b12C when the sensitivity corresponding to the light ray 2a is set to 1. As shown in the table below, the ratio of sensitivity to the R component and the B component differs depending on the angle of incidence.

Table 1 Light rays B channel 2a 1 2b 1 2c O, 7 R channel 0.5 1.5 An image is formed by a collection of light rays that have passed through the color separation film at various incident angles. Therefore, even if the gains for the R and B components are adjusted so that faithful color reproduction can be obtained in a certain group of light rays, the color balance will be disrupted in a different group of light rays. For example, if you adjust the color balance with respect to the center of the screen when the image is in focus, ■ the edge of an achromatic subject in the defocused area will be affected by Color shading occurs for achromatic subjects.

In order to prevent such a phenomenon, the present invention disposes the interference film (34) closer to the RB component light output side than the color separation film (32), as shown in FIG. At this time, the interference film (34
) is used that has the same spectral characteristics as the color separation film (32), and the color separation film (32) and interference film (34) are arranged so as to be inclined in opposite directions with respect to the optical axis. Therefore, the light rays (3a), (3b), which are incident on the color separation prism (30),
The spectral transmittance of the color separation film (32) for (3c) is the transmittance curves (4a), (4b), and (4) in FIG. 4, respectively.
Corresponding to C), the spectral transmittance of the interference film (34) corresponds to (4a), (4c), and (4b) in the figure, respectively. For example, the light beam (3b) incident on the color separation film (32) is transmitted through the color separation film with the spectral transmittance shown in (4b) in FIG. It passes through the interference film (34) with the spectral transmittance shown in (4c).

The light beam emitted from the color separation prism of the present invention reaches the solid-state image sensor (15). The spectral sensitivities of the R channel and B channel of the imaging system in this case are as shown in FIG. The same curves result for rays (3b) and (3c). Furthermore, the sensitivity depending on the angle of incidence is as shown in Table 2 below.

Table 2 Light ray B channel R channel 3a 1 1 3b O,70,6 3c O,70,6 From Table 2 above, the difference in the sensitivity ratio for the R component and the B component depending on the incident angle is small, and the defocus part It can be seen that the color imbalance around the screen is reduced.

Also, when comparing Figures 6 and 7, we see that the rays (3b) and (3b)
The sensitivity corresponding to C) is considerably lower than the sensitivity corresponding to light rays (2b) and (2C), but the sensitivity corresponding to light ray (3a) is almost lower than the sensitivity corresponding to light ray (2a). do not have. Therefore, the decrease in sensitivity of the entire luminous flux is limited to about 10 to 20%. Furthermore, since the shape of the spectral characteristics is good, an imaging system with good color reproducibility can be obtained.

Comparative Example In order to achieve the same problems as those of the present invention, a trimming filter having spectral characteristics as shown in FIG. 8 was placed between the color separation prism and the solid-state image sensor (15).

The spectral sensitivities of the R channel and B channel of the imaging system in that case are shown in FIG. 9, and the sensitivity ratios are shown in Table 3 below.

Table 3 Light ray B channel R channel 2a 1 1 2b 1 0.8 2c O,81 From Table 3 above, the difference in sensitivity ratio between R component and B component depending on the incident angle is small, and the difference in the sensitivity ratio of the achromatic object in the defocused area is small. It can be seen that color shading is less likely to occur for achromatic subjects at the edges and the periphery of the screen (color balance is not disrupted).

However, when comparing FIG. 6 with FIG. 9, the absolute sensitivity is reduced to about half of the original sensitivity due to the trimming filter. Furthermore, the spectral sensitivity characteristics deviate greatly from the ideal, resulting in an imaging system with poor color reproducibility.

Comparing the present invention and a comparative example, it is found that the color balance of the edge part of the defocusing part and the peripheral part of the screen is better in the present invention than in the comparative example using a trimming filter (Table 3). It can be seen that the difference in the sensitivity ratio for the components is small, so it is improved.

Effects of the Invention According to the present invention, a color separation prism is used in which an interference film having the same spectral characteristics as the color separation film is disposed between the color separation film and the solid-state image sensor, tilted in the opposite direction to the color separation film with respect to the optical axis. By doing so, the color balance of edges in the defocused portion of the screen and the color balance of the periphery of the screen are improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of an optical system of a solid-state imaging device using color separation prisms. FIG. 2 is a diagram showing an example of a schematic configuration of a color separation prism according to the present invention. FIG. 3 is a diagram showing a schematic configuration example of a conventional color separation prism. FIG. 4 is a diagram showing the spectral transmittance of the color separation film. FIG. 5 is a diagram showing the spectral sensitivities of the R channel and B channel of the solid-state image sensor. FIG. 6 is a diagram showing the spectral sensitivities of the R channel and B channel of a solid-state image sensor when a conventional color separation prism is used. FIG. 7 is a diagram showing the spectral sensitivities of the R channel and B channel of a solid-state imaging device when the color separation prism of the present invention is used. The eighth factor is a diagram showing the spectral transmittance of the trimming filter. FIG. 9 is a diagram showing the spectral sensitivities of the R channel and B channel of the solid-state image sensor when a trimming filter is used.

Claims (1)

[Scope of Claims] 1. In a color separation prism used in a multi-plate imaging device, which separates an incident light beam into a plurality of light beams according to wavelength, the color separation prism splits the incident light into at least a green component and a magenta component. It consists of a color separation film that separates the light into magenta components, and an interference film placed on the magenta component light output side of the color separation film.The interference film has the same spectral characteristics as the color separation film, and the color separation film and interference film are on the optical axis. A color separation prism characterized in that it is arranged and configured so that it is tilted in the opposite direction.